一道英语问题1.Which of the floolwing sentences is not correct?.A.I

一道英语问题
1.Which of the floolwing sentences is not correct?.
A.I saw an accident while I was walking to school.
B.There was an accident happened yesterday morning.
C.Great changes have taken palce in Shenzhen.
D.There was a fire burning in the fireplace.
如何选择这四个答案,